I use calibre web for this. It is a bit funky to setup though depending on your level of experience. Here’s a guide to look over https://jccpalmer.com/posts/setting-up-kobo-sync-with-calibre-web/

This is where I’m at too. Mostly just to handle download processing in a better way, most of my searches are still manual but I’m trying to be ready for the chaptarr release.

Running calibre with some stuff to auto convert to kepub and calibre web for Kobo sync.

Finally getting around to setting up a reverse proxy this weekend.

Any good ways of getting the Kobo sync working externally?